Several forms of cytochrome P-450 are known to exist in mammalian liver. The type and amount of these "cytochromes P-450" present are affected by exposure of the animal to some drugs, polycyclic hydrocarbons, and various other substances in the environment. Cytochrome P-450 is the rate-limiting component of a mixed-function oxidase enzyme system which catalyzes the metabolism of many compounds including a large number of those polycyclic hydrocarbons known to produce cancer in humans. The ability of the individual to activate or de-activate chemical carcinogens and thus his susceptibility to cancer induction by a given agent may depend on the absolute amounts of relative proportions of particular cytochrome P-450 species present. Hence, it would be useful to be able to recognize and quantitate the cytochrome P-450 forms. In this study methods for the identification of these proteins are being developed. These methods include: 1) SDS-polyacrylamide gel electrophoresis, 2) isoelectric focusing, and 3) spectrophotometric examination. The methodology is being developed using rat and rabbit liver. Once established, the methods will be applied to analysis of cytochromes P-450 of human blood monocytes and lymphocytes.